1. Field of the Invention
This invention relates generally to the agglomeration of particles and, more particularly, to an agglomerator that separates particles by size into two groups and electrostatically induces an opposite charge to each of these groups to facilitate the agglomeration of the smaller particles to the larger particles.
2. Description of the Related Art
A variety of systems are known for collecting, detecting and/or filtering of particulate matter in flow streams of gases, liquids, and porous solids. These systems are used in a variety of ways: to clean air in an enclosed environment, to filter impurities from flow of combustible liquid, to detect the presence of certain particles, to collect particles from an exhaust flow for recombustion, as well as other uses. With respect to the collection of particles, inertial-based collection is regarded as the only viable technique in some systems, especially those requiring a low pressure drop, in-line separation, or collection into a liquid matrix for subsequent analysis, while still collecting relatively small particles, including submicron particles. For example, real-time or near real-time biological warfare detection systems most often require collected particles to be contained in a liquid sample. However, known inertial-based liquid collection systems, as well as electrostatic precipitators, while relatively efficient at collecting large particles (greater than about 2 micrometers, or 2 microns) have a poor collection efficiency for smaller particles, especially sub-micron particles. Thus, in many applications, no reliable solution exists for collecting such small particles.
The use of agglomerators is known for grouping small particles together to make such particles easier to collect. Unfortunately, this process is inefficient when small particles are grouped together with other small particles as they take a substantial amount of time to agglomerate to a sufficient size. Further, even if a significant number of small particles agglomerate, they may still be insufficiently sized in a certain dimension, making collection difficult.
To improve such agglomeration, it has been proposed to use bipolar charging on small and large size particles by giving each size group an opposite polarity. However, the prior art fails to teach a system for reliably separating a gas flow into streams of different sized particulate matter, imparting opposite electrical charges on the streams, and subsequently reintroducing the streams together downstream of the charging region to facilitate agglomeration of small particles to the large particles.
A device for agglomeration of particles in a gaseous flow is proposed in U.S. Pat. No. 6,224,652 of Caperan et al. A gaseous flow containing particulate matter is introduced into an inlet and an electrical charge of a given polarity is applied. The flow is then joined by a feedback loop of particles of a larger aerodynamic diameter having a charge of an opposite polarity and proceeds to the agglomeration chamber. An extraction unit acts as a separator to remove a gaseous flow containing larger particles for the feedback loop and send a gaseous flow containing small particles to the outlet of the device. The introduction of the feedback loop is said to further enhance the agglomeration process as smaller particles in the inlet flow are exposed to an increased concentration of larger particles.
Despite the benefits provided by the Caperan et al. device, it suffers from distinct disadvantages. Because larger particles are intentionally recirculated in the system with no mechanism for their removal, buildup of agglomerated particles occurs. While buildup of larger agglomerates will improve the agglomeration efficiency, it will also eventually obstruct flow in the system. Furthermore, because of the lack of a way to remove the agglomerated particles, sampling and analysis of the attached small particles is difficult and recirculation of the agglomerated particles will cause contamination in the system.
Another system for separating and removing particles from a gas or fluid stream is disclosed in U.S. Pat. No. 5,972,215, of Kammel. The system uses a precleaner, an agglomerator, a high-efficiency particle separator, a medium-efficiency particle separator, and a final particle separator to progressively clean the fluid stream of unwanted particles. Electrically charged augers may be provided in the precleaner to coagulate small particles on the surface of the augers. Once the coagulated particles reach a certain size, they are cast back into the flow stream for further separation. The agglomerator is formed of a wire mesh divided into positively and negatively charged packs. This configuration is said to enhance the diffusion and interception modes of particle collection. Additionally, the high-efficiency particle separator is equipped with louvers each having an opposite polarity to form an electrostatic field to enhance collection performance. However, Kammel requires a complicated series of filtering and separating devices and does not provide a system for enhanced preferential agglomeration of small particles onto larger xe2x80x9ccarrierxe2x80x9d particles for increased collection efficiency. Thus, the agglomeration in Kammel only modestly increases the size of the particles of interest.
Thus, what is needed is a particle agglomerator for a gas or fluid flow stream that facilitates the agglomeration of a number of small particles onto larger xe2x80x9ccarrierxe2x80x9d particles through electrostatic attraction to provide for better collection of the particles, analysis of the flow stream, and formation of agglomerated particles of a sufficient size to be reintroduced for more complete combustion. The agglomerated particles would include both solid particulate matter, liquid droplets, and small organisms. The device should be configured to accept a flow stream of both small and large particles or a flow stream of only small particles into which larger particles can be later introduced.
It is an object of the present invention to provide an agglomerator with electrostatic characteristics for the agglomeration of small particles onto larger xe2x80x9ccarrierxe2x80x9d particles. It is a further object of the present invention to provide such a device configured to separate a flow stream into two flow streams, one containing small particles and the second containing larger particles, for imparting opposite electrical charges on each of the flow streams to aid in the electrostatic attraction of the particles for agglomeration. It is yet a further object of the invention to provide such a device that collects the agglomerated particles for further analysis or processing. It is still a further object of the present invention to provide such a device that exhausts out the flow stream with a minimal amount of particles present. It is also an object of the present invention to provide multiple agglomerators in series to further improve the efficiency of agglomeration. It is yet another object of the present invention to provide such a device that is simple to use, efficient in operation, and achieves sufficient agglomeration of small particles while only having a minimum amount of moving parts.
The present invention provides a size preferential electrostatic agglomerator that separates particle into different flow streams for imparting opposite electrical charges on each stream to maximize the agglomeration and collection of the small particles with larger xe2x80x9ccarrierxe2x80x9d particles. The device comprises an inlet for receiving a flow of a gas into a chamber, a separator positioned in the chamber for separating the gas flow into first and second gas flow streams, the separator having a primary pathway in which the first gas flow stream comprised primarily of smaller particles is directed and a secondary pathway in which the second gas flow stream comprised primarily of larger particles is directed, an ionization region positioned in the chamber and downstream of the separator for receiving the gas flow, the ionization region having a first charging area within the primary pathway to impart an electrical charge on the smaller particles and a second charging area within the secondary pathway to impart an opposite electrical charge on the larger particles, an agglomeration region positioned in the chamber and downstream of the ionization region configured to receive the first and second gas flow streams and facilitate the agglomeration of smaller particles with the larger particles, and an outlet for exhausting the flow of gas out of the chamber. The larger particles can be of the type typically present in the gas flow or can be xe2x80x9cseedxe2x80x9d particles added to the flow.
In another aspect, a secondary separator can be added downstream of the agglomeration region of the present invention to separate the agglomerated particles from the major gas flow exhausted through the outlet to facilitate analysis or processing of the agglomerated particles. Whether or not the secondary separator is utilized, an inertial based sampler can be coupled to the present invention to receive the agglomerated particles. Additionally, multiple agglomerators can be placed in series to progressively agglomerate more of the smaller particles to the larger particles and improve collection efficiency.
In yet another aspect, the ionization region can be positioned in only one of either the primary or secondary pathway if the particles in the opposite pathway are already provided with a polarization. Thus, the particles travelling through the pathway having the ionization region would be imparted with an electrical charge opposite of the charge held by the particles travelling through the pathway without an ionization region.
Thus, the present invention provides improved collection efficiencies for relatively small particles by facilitating the larger particles becoming oppositely charged xe2x80x9ccarrierxe2x80x9d particles for electrostatic attraction. In this way, the agglomeration of a larger amount of the small particles on the larger particles aids in collecting, detecting, and performing other functions on the small particles.